Bosch Common rail

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Bosch Common rail

Fuel injection system components

Fig. 1

  1. 3rd piston cut-off solenoid
  2. Accelerator position (APP) sensor
  3. Battery
  4. Crankshaft position (CKP) sensor
  5. Engine control module (ECM)
  6. Engine coolant temperature (ECT) sensor
  7. Exhaust gas recirculation (EGR) solenoid
  8. Fuel cooler
  9. Fuel filter
  10. Fuel heater
  11. Fuel injector
  12. Fuel lift pump (electrical)
  13. Fuel lift pump (mechanical)
  14. Fuel lift pump relay
  15. Fuel pressure control solenoid
  16. Fuel pressure sensor
  17. Fuel rail
  18. Fuel shut-off solenoid
  19. Fuel tank
  20. Fuel temperature sensor
  21. Glow plug relay
  22. Glow plug
  23. Glow plug warning lamp
  24. High-pressure fuel pump
  25. Ignition switch
  26. Intake air temperature (IAT) sensor
  27. Malfunction indicator lamp (MIL)
  28. Manifold absolute pressure (MAP) sensor
  29. Mass air flow (MAF) sensor
  30. Turbocharger (TC) wastegate regulating valve
  31. Vehicle speed sensor (VSS)

System operation

The Bosch Common rail system uses the latest diesel injection technology.

The fuel injection quantity and timing together with control of exhaust emissions are electronically controlled.

Signals from the accelerator pedal position (APP) sensor [2] together with information from other engine and vehicle sensors are transmitted to the engine control module (ECM) [5].

An electrical fuel pump [12] or an engine driven mechanical pump [13] or both supply fuel at low pressure to the high-pressure pump.

The high-pressure fuel supply is provided by an engine-driven mechanical high-pressure pump [24]. The pump comprises three pumping elements driven by an eccentric shaft.

The pressure is controlled by a fuel pressure control solenoid [15] mounted on the rear of the pump.

On some applications a 3rd piston cut-off solenoid [1] is used to enable the pump to operate only two pumping elements, resulting in less engine power being absorbed at low engine loads.

High-pressure fuel from the high-pressure fuel pump is delivered to the fuel rail [17] where it is distributed to the injectors [11]. Operating conditions in the fuel rail are monitored by the fuel temperature sensor [20] and fuel pressure sensor [16].

The fuel injectors are electrically operated by the ECM [5] and use low-resistance solenoids. To reduce the current being switched by the ECM, the voltage is rapidly switched during the injection period.

The fuel is injected in two stages (or three where exhaust emission standards are higher), firstly the PILOT injection to precondition the combustion chamber, followed very shortly afterwards by the MAIN injection. Some applications where higher exhaust emission standards are required use a third period of injection called POST injection, where fuel is injected into the exhaust stroke and reburnt via the exhaust gas recirculation (EGR) system.

Subpages (1): Bosch in-line with EDC
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